The invention relates to a process and a system for controlling the longitudinal dynamics of a motor vehicle.
A process and a system of this generic type are disclosed in German patent document DE 196 32 337 A1. In that System, the longitudinal dynamics are controlled by a drive train actuating signal, and optionally also by a brake system actuating signal. The two actuating signals are generated by a two-stage longitudinal dynamics controller which includes a first stage for determining controller-internal values for the desired longitudinal velocity and the desired longitudinal acceleration. A second stage connected behind the first stage uses the fed controller-internal desired longitudinal velocity values and desired longitudinal acceleration values as well as fed input data concerning the actual driving condition to compute the drive train actuating signal (and optionally the brake system actuating signal) by means of an inverse vehicle longitudinal dynamics model. The vehicle longitudinal dynamics model contains an engine model which determines from an input drive train actuating signal the engine torque supplied by the engine and the rotational engine speed as input quantities for an automatic transmission and rear axle model unit connected downstream. The latter determines therefrom a wheel driving torque applied to the driving wheels and the pertaining rotational wheel speed. In parallel thereto, a brake system model unit determines a pertaining braking torque from the supplied brake system actuating signal. The automatic transmission and rear axle model unit contains a model of a torque converter and of a multi-step reduction gear, the torque converter being assumed to be a hydrodynamic clutch, in which the torques are transmitted by a fluid between the pump wheel and the turbine wheel.
In contrast to other conventional systems, such as that described in German patent document DE 43 38 399 A1, this system has the advantage that it better takes into account the nonlinear behavior of the vehicle. This is of considerable significance particularly at low driving speeds and in the case of greater longitudinal road slopes or at different vehicle loads. It is particularly beneficial in the case of trucks, and also in range control systems, such as range cruise control systems for medium and high driving speeds as well as stop-and-go vehicle follow systems for low driving speeds, in which a longitudinal dynamics control circuit is subordinate to a range controller. From the measured range and the relative speed, the superimposed range controller determines a desired acceleration for the subordinate longitudinal acceleration control circuit. The range control becomes more precise when the subordinate control circuit compensates for non-linear vehicle handling characteristics because the design of the range controller can then be based on a linear vehicle behavior. Although the system according to German patent document DE 196 32 337 A1 takes these demands into account, this requires either that a sufficiently precise inverse vehicle longitudinal dynamics model exists, or that one can be set up. This is not ensured in all cases. In addition, this known approach requires a relatively large amount of computing power for continuous computations within the inverse vehicle longitudinal dynamics model.
One object of the invention is to provide a longitudinal dynamics control process and a system of the initially mentioned type which takes into account the non-linear vehicle longitudinal dynamics behavior with a satisfactory precision.
Another object of the invention is to provide such a process and system which require comparatively low computing expenditures for this purpose.
These and other objects and advantages are achieved by the process and apparatus according to the invention, in which the drive train actuating signal and optionally the brake system actuating signal are determined from actual driving condition data as well as from the controller-internal desired longitudinal acceleration values and desired longitudinal velocity values, by means of an inverse characteristic vehicle longitudinal dynamics diagram. Such a diagram can, for example, be determined beforehand by means of corresponding test drives from measured data recorded during these drives. In continuous driving, the use of such an inverse characteristic vehicle dynamics diagram requires significantly lower computing expenditures than the use of an inverse vehicle longitudinal dynamics model. In addition, this approach requires no knowledge concerning the behavior or the current condition of a transmission torque converter and of the engine. On the contrary, a desired drive train actuating signal is determined from the input data, such as those concerning the actual driving condition, controller-internal longitudinal velocity values. The drive train actuating signal can then be derived from the desired drive train actuating signal.
In one embodiment of the invention, the actual driving condition data taken into account contain data concerning the transmission ratio, the vehicle mass and/or the road slope. As a result, corresponding influences of the currently engaged transmission shifting position, and current vehicle loading and road slope can adequately be taken into account for the determination of the drive train actuating signal.
Another embodiment of the invention limits the controller-internal desired longitudinal velocity value (determined from the desired longitudinal acceleration and the actual longitudinal velocity) to a definable tolerance band around the actual longitudinal velocity. This feature avoids undesirably high jolt-type accelerations at larger speed deviations.
In still another embodiment of the invention, a brake system actuating signal is determined in addition to the drive train actuating signal. Both actuating signals are advantageously derived from the desired drive train actuating signal of the inverse characteristics vehicle longitudinal dynamics diagram such that the drive train or the brake system is appropriately activated in any situation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.